New 3D Printable Stent Holds Promise for Tracheal Tumors

Pam Harrison

March 09, 2022

Airflow obstruction caused by a malignant tracheal tumor may be managed with a uniquely designed, 3-dimensional (3D) drug-eluting tracheal stent that, at least in animal models so far, works well and may soon be ready for human trials, Chinese investigators are reporting.

The research was published online January 29 in Materials Today Chemistry.

The problems with currently available stents used to treat airflow obstruction are considerable, corresponding author Shengrong Guo, PhD, professor of pharmaceutics, Shanghai Jiao Tong University, Shanghai, China, and colleagues observe. "Tracheal stents physically open up stenosis, recover airway patency, and promptly relieve symptoms but [they] cannot treat the tumor," they explain.

"Thus, tracheal restenosis always occurs soon [after] due to progressive tumor growth after stent placement," they add. Moreover, implanted stents cover the entire tracheal mucosa, thus preventing mucus and sputum discharge, causing airway blockage, the investigators also note. Compounding these flaws is the unalterable fact that delivery of chemotherapy to a malignant tracheal tumor is inefficient, and systemic chemotherapy is always associated with systemic side effects.

All of these issues make it very challenging to treat these tumors, Guo noted. On the other hand, if there were a means to deliver a chemotherapeutic agent more directly to the disease site — as is done with drug-eluting beads, for example, in other tumor types — then at least drug delivery would be much more efficient. "In this study, a novel tracheal stent was designed with features of a C-shaped and trilayered wall," the researchers explain.

The gap angle of the newly developed stent is 72°; the inner diameter is 0.5 cm, and it is 2.0 cm in length. The trilayered wall consists of an inner layer of poly (ε-caprolactone) (PCL), which is a biodegradable and implantable material used alone or compounded with other ingredients to print implants. The middle layer consists of magnetic nanoparticle (MNP)–loaded PCL. The authors explain that MNPs have been approved in the US as contrast agents in MRI.

Combined with temperature-responsive materials, MNPs can serve as a source of magnetic thermotherapy as well, which can be used to control drug release and facilitate drug penetration into deeper tissues. The outer layer of the stent contains a paclitaxel-loaded ethylene-vinyl acetate copolymer layer.

"The C-shaped tracheal stents are easily fabricated on a roller by using a self-made specific three-dimensional printer," the authors explain. They point out that the C-shaped tracheal stents do not cover the entire tracheal wall, and the uncovered gap in that wall allows for normal mucus and sputum discharge.

In Vivo Evaluation

Once the stents were printed, the researchers evaluated the biosafety and applicability of their C-shaped tracheal stents. Small rabbits weighing 2.5 to 3.0 kg were used as experimental models and were prepared for surgery. The stent was implanted in the rabbits' trachea through the use of a simple stent delivery device. During follow-up, the rabbits recovered well without any sign of infection or respiratory complications.

The animals were also eating well within about 5 days of the surgery, and their weight gradually increased, suggesting that the implantation of a stent with intermittent magnetic heating did not lead to any prominent systemic toxicities. "All rabbits were [euthanized] 30 days after the placement of the tracheal stents" and the stent was removed from the rabbits' trachea, the researchers report.

Close observation of the trachea indicated that the gap left by the C-shaped stent could keep the airway patent without blocking either mucus or sputum discharge. "The stents have good biosafety in rabbits and keep airway patency for 1 month without the occurrence of mucus/sputum blockage after implantation in rabbit trachea," Guo and colleagues conclude.

"These results provide a scientific basis for the development of novel self-expandable C-shaped tracheal stents with combinatorial tracheal support and local chemotherapy," they affirm.

Pediatric Airway Obstruction

Thus far, the role of 3D printing seems to be most prominent in the treatment of pediatric airway obstruction, where it is used in the surgical planning stages and to create the implant itself. In a systematic review of its use for this, Joshua Stramiello, MD, University of California, San Diego, and colleagues identified 37 original articles, 11 of which discussed 3D printing for surgical planning and 26 of which discussed 3D printing implants for interventions.

"3D printing for surgical planning not only improves pre-operative assessment of surgical approach and stent customization but also helps facilitate patient/family education," the authors observe. Most of the research so far has been focused on bioresorbable external airway splints and biological grafts, they add — "with both animal studies and human case reports showing good results in improving symptoms," the authors conclude. One clinical series focused on the use of a 3D-printed, patient-specific, bioresorbable airway splint in a cohort of critically ill children with severe tracheobronchomalacia. (Tracheobronchomalacia is the abnormal collapse of the windpipe).

When reported, 29 splints had been implanted in 15 children with intrathoracic tracheobronchomalacia. At a median follow-up of 8.5 months, 12 children were long-term survivors, and all but one lived at home. As recently discussed by George Cheng, MD, cofounder of restor3D, a Duke University startup that created the first 3D-printed airway stent using a compressible biocompatible material with properties similar to that of silicone, personalized airway stents have the potential for advance customization, minimize pressure points, and improve airflow dynamics to increase mucus clearance.

In fact, the US Food and Drug Administration has already cleared patient-specific airway stents developed by Thomas Gildea, MD, of the Cleveland Clinic. Both the Duke University and Cleveland Clinic stents have been used in patients, with promising outcomes, Cheng noted.

The authors and Stramiello and colleagues have disclosed no relevant financial relationships. Cheng is the cofounder of restor3D.

Mater Today Chem. Volume 24, June 2022. Abstract

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